Got the idle fine, but no power beyond 2K RPM?

[Russ]

Hi all;
Hope ya had a good Christmas.
(Early S-Man, thanks for the jetting info)

Car: '72 911E with 40IDA3C webers

I bought the car and it ran like crap at idle, but didn't miss so much when you got it out on the road at mid and high rpm (though it still popped and sputtered).
Did work on the carbs and now it purrs at idle but when under load it cant get past about 3500 RPM. Completely gutless.


Details:
Dwell is 37 degrees. Plugs are new W7DC.
I took the carbs apart and cleaned everything. I reassembled them without the body gaskets (Will this cause a problem?) as the PO had covered the gaskets with white paint?... All the idle jets are 60 (They say 60, and I am borowwing a set of jet gauges to make sure) and the mains are 135. F26 emulsions with 180 air correction.
I misread the manual and adjusted the float tabs way too low, so fuel spilled everywhere. Took them apart and got them back close to where they should be. Am borrowing a screw on float level gauge to check. Could bad float level cause this kind of a problem or should I check something else? Also, where can you get spacer shims for under the float valve so I can adjust them as needed? Has anyone found other washers that work?

Thanks, Russ

[911pcars]

Russ,
If the float level isn't real low, check the fuel pump for pressure and volume. I'm not sure how low the fuel level in the float chamber can go to create the symptom you have. You'll have a better idea of your troubleshooging direction after installing the weber float gauge.

Besides PMO, Otto's and Motor Meister have said they carry Weber parts.

Regards,
Sherwood Lee
http://members.rennlist.org/911pcars

[john walker's workshop]

the primary venturis can be installed backwards if you're not careful, blocking any mainjet fuel to that cylinder. make sure the fuel outlet in the center of the small venturi tube is on the same side as the emulsion tube/air corrector for that cylinder. is the mechanical advance free?

[Early_S_Man]

I don't quite understand why so many of you with drastic power losses always worry about the dwell, and NEVER about the advance curve? The CDI-unit will trigger and work perfectly well on points that are way out of spec on dwell!

However, the advance curve ... meaning how much advance at various rpm levels -- is highly critical on a 911 engine!!! And, it affects both power and how high the engine will rev without bogging down, under load!

[J P Stein]

I missed this in the first read thru of your post..


" I reassembled them without the body gaskets (Will this cause a problem?) as the PO had covered the gaskets with.........."


Do you mean the gasket between the top and body?

[Russ]

Yes,
The gasket between the body and the tops. The PO had covered them with white paint that was coming off in flakes and probably jamming the passages. I didn't have a rebuild kit, so I just put the top back on without the gasket. They dont seem to need a seal because they vent directly to the atmosphere, but is there something else I am not thinking of?
Before, the car ran like crap at idle and on acceleration (popping, missing), but at higher rpm with a steady throttle it ran ok. So I assume the advance is OK, but will pull the distributor and get it properly tested.
Other question: Is there any way to determine which pistons are in an engine without disassembling it. I could use a borescope to look at them (to check for burning if nothing else), so am wondering if there is a difference in the crown that may identify them. Did a compression test and most are 140, one at 155, and one of them I could get the damn compression gauge to screw into. Is 140 acceptable? and does it say anything about the possible pistons. The reason I am wondering is that in the pile of receipts one of it's previous rebuilds (second to the last) says they put in S pistons. Curious of possible implications.
Thanks to both of you for answering this thread

Russ

[J P Stein]

I would think that thoses gaskets are required, not optional.

A fresh start would seem to be in order here.
I would suggest buying a couple of rebuild kits and replacing all
gaskets, O rings, acc pump diaphrams, etc.

HTH

[911pcars]

I believe the gasket is there mainly to keep gas from sloshing out of the fuel bowl past the joint. However, since the top of the carb houses the needle and seat and the float is in the float bowl, the thickness of a gasket or a lack of one will affect the float level. However, not sure how low a fuel level will create the symptoms you have. Have you measured the fuel pressure, volume and carb fuel level yet?

Lets' do the most likely and easy troubleshooting stuff first.

Sherwood Lee

[T Bird]

A low fuel level can affect top end performance. The fuel level in the bowls determines when fuel is introduced into the main circuits. The transition between idle and main circuits occurs around 3000-3500 RPM, the speed where you indicate the engine runs out of steam. Thus, too low a fuel level will keep the main circuits from operating, preventing your engine from operating above 3500 RPM.

The expedient fix would be to check/adjust the float levels with Porsche tool P226a, available from PMO. The gauge comes with the spacers. If this were my car, I would follow the advice given above and do a complete rebuild. A rebuild kit runs about $80 from PMO.

Good luck.